The removal of Cu(II)-EDTA chelates using green rust adsorption combined with ferrite formation process

Classical adsorbents such as activated carbon are inefficient to remove Cu(II)-EDTA in solution. Moreover, the heavy metals in the generated sludge can easily be dissolved back into solution. In this research, a novel strategy developed by coupling green rust adsorption and ferrite formation technology was proposed for Cu(II)-EDTA chelate removal. At the adsorption stage, green rust sulfate (GR_ME(SO₄^2-)) showed a high adsorption efficiency of chelated copper, with a capacity of 126.41 mg g^-1, compared to other classical adsorbents. During the ferrite formation stage, GR_ME(SO₄^2-)-based precipitate with high moisture content and slow settling rate could be transformed into ferrite-based precipitate with low moisture content and rapid settling rate. The volume and moisture content of ferrite were 2.20 and 1.45 times lower than those of GR_ME(SO₄^2-) and the sedimentation velocity of ferrite was also 1.23 times higher than that of GR_ME(SO₄^2-), which strongly demonstrated the necessity of the ferrite formation process. Toxicity characteristic leaching procedure (TCLP) test results showed that the metallic copper of GR_ME(SO₄^2-) sludge could be more easily dissolved back into solution than that of ferrite precipitate under weak-acid conditions, indicating the stability of ferrite. In addition, after the ferrite process, the generated sludge exhibited soft magnetism and could be quickly separated within few seconds using an external magnetic field. All these results showed that the combined green rust adsorption with ferrite formation method was an efficient, recyclable and eco-friendly method for the treatment of wastewater containing Cu(II)-EDTA.